Media players and personal computers that can play large-capacity optical disc media such as DVDs are now in wide use, and high-quality game contents and image contents, which are stored in DVDs and the like, are on offer. Also, using a DVD recording device incorporated in a DVD recorder or a personal computer, the user can readily record photos, videos, etc., on DVDs.
Also, Blu-ray Disc (BD: trademark or registered trademark) has been developed as an optical disc medium that can record hi-vision-class images and game contents, and it has begun offering fascinating contents of high image quality.
There are also game devices that have the function of reading out and playing image contents stored in an optical disc (See Patent Document 1, for instance).
[Patent Document 1] U.S. Pat. No. 6,563,999.
When an optical disc, such as a CD (Compact Disc) or a DVD, is to be accessed, the head including an optical pickup unit must be moved to the reading position, and this takes a seek time and a time for reading the file. A drawback in this is that the file system recorded on the optical disc takes a longer access time than the file system on a hard disk.
This problem of read rate with the optical disc is not so much felt when the disc with a music or video content is being played. This is because, with music or video, a single file of a large size is read out continuously, so that while the user may be conscious of the wait time before the start of playing, the latency for reading data will be covered up once the playing starts.
However, with an optical disc storing game content, various files are opened and read not only at the starting of a game application but also during the progress of the game. As a result, there are often waitings for access to the optical disc during the play of the game. Also, the individual files handled by the game application are small in size, and the files are accessed in a pattern similar to that of random access. This increases the seek time for the optical disc. Therefore, a problem with an optical disc having game contents recorded thereon is the access time to the optical disc that can sometimes have a negative effect on the real-timeliness of the game.
Also, BD employs a method of recording information in a plurality of layers in a similar manner to DVD. And with BD in particular, it is absolutely imperative that the depth of focus be finely adjusted using a servo motor while directing a laser beam to accurately adjust the depth of focus of the laser beam to a recording layer of high density. As a result, there is much load on a drive system in a pickup unit of the optical disc.
The present invention has been made in view of these problems and a purpose thereof is to provide a disc access technology for efficiently accessing a file system recorded on a disc medium.